mozjs_sys: Honor the CXXSTDLIB environment variable (#615)

`CXXSTDLIB` is an environment variable used by `cc` and many other
crates which lets developers to choose a standard C++ library of their
choice.

Make use of that variable in mozjs_sys's build.rs as well.

One of the use cases is supporting Linux distributions which use LLVM
instead of GCC as the main toolchain (e.g. Chimera, Gentoo musl-llvm
profile, OpenMandriva).

Signed-off-by: Michal Rostecki <[email protected]>

Author: vadorovsky

mozjs-sys/Cargo.toml

@@ -2,7 +2,7 @@
 name = "mozjs_sys"
 description = "System crate for the Mozilla SpiderMonkey JavaScript engine."
 repository.workspace = true
-version = "0.137.0-2"
+version = "0.137.0-3"
 authors = ["Mozilla"]
 links = "mozjs"
 license.workspace = true

mozjs-sys/build.rs

@@ -386,13 +386,15 @@ fn link_static_lib_binaries(build_dir: &Path) {
         println!("cargo:rustc-link-lib=user32");
         println!("cargo:rustc-link-lib=Dbghelp");
         println!("cargo:rustc-link-lib=advapi32");
-        if target.contains("gnu") {
-            println!("cargo:rustc-link-lib=stdc++");
-        }
+    }
+    if let Some(cxxstdlib) = env::var("CXXSTDLIB").ok() {
+        println!("cargo:rustc-link-lib={cxxstdlib}");
     } else if target.contains("apple") || target.contains("freebsd") || target.contains("ohos") {
         println!("cargo:rustc-link-lib=c++");
-    } else {
+    } else if target.contains("windows") && target.contains("gnu") {
         println!("cargo:rustc-link-lib=stdc++");
+    } else if !target.contains("windows") {
+        println!("cargo:rustc-link-lib=stdc++")
     }
 }